Driver for electroacoustic transducers



Aug. 13, 1946. H. c. HAYES ETA L DRIVER FOR ELECTRO-ACOUSTIC TRANSDUCERS Filed Nov. 28, 1941 Liza-.5

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Ara/1r Patented Aug. 13, 1946 DRIVER, FOR ELECTROACOUSTIC TRANSDUCERS Harvey C. Hayes and Harold L. Saxton, Washington, D. C.

Application November 28, 1941, Serial No. 420,853

(Cl. 177 352) w (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) 8 Claims.

This invention relatesv to a means for driving an electro-acoustic transducer by the application of a series of short spaced pulses of power. The driver of the invention is of the impulse type capable of delivering a large amount of power to the transducer during a short interval of time and then automatically becoming electrically isolated therefrom during a longer interval of time, during which the transducer is free to oscillate at its own natural mechanical frequency.

The driver of the invention possesses many advantages over the types of drivers now in use, the realization of which may be considered as being among the objects of the invention. One these advantages is the. fact that the driver does not affect the frequency of oscillation of the transducer except during the brief interval of time during which it is supplying power. A further advantage is the fact that the power is supplied in a single uni-directional pulse thereby reducing the tendency for the transducer to feed energy back to the driver, and thereby reducing losses in the driver itself. Still another advantage of this invention arises from the supplying of pulses at periodic intervals which results in the modulation of the output of the transducer at a predetermined frequency.

Other objects will appear from a consideration of the following description and the accompanying drawing, in which Fig. 1 is a circuit diagram of one form of the invention and Fig. 2 is a circuit diagram of a modified form of the invention.

Referring now to Fig. l of the drawing:

Unit IA is one form of charging circuit for condenser Cm while unit [3 is one form of discharging circuit for condenser Cm. The condenser Cm thus stores energy momentarily between that part of the cycle during which it is charged and that part of the cycle during which it is discharged. Condenser Cm is a part mutually of both the charging circuit and the discharging circuit. One side of Cm is grounded.

In unit IA, V1 is a mercury vapor rectifier tube, T1 is a filament transformer for said tube, T2 is a plate supply transformer for said tube and R1 is a resistor. The tube V1, the secondary of transformer T2 and the resistor R1 are connected in series with each other and with the condenser Cm, and these parts together comprise the circuit through which the charging of Cm takes place.

In unit IB, V2 is a mercury vapor rectifier tube provided with a control grid, T3 is a filament transformer for said tube, T4 is a grid biasing transformer, C2 is a condenser, and R2 and Rs are resistors. The anode to cathode circuit of tube V2, the transducer it] to'which power is to be supplied, and the condenser C2, are connected in series with each other and with the condenser Cm, and these parts together comprise the circuit through which the discharging of Cm takes place. Resistor R2 is shunted across C2. The grid of tube V2 is connected through resistor R3 and the secondary of transformer T4 in series with said resistor, to the opposite side of condenser C2 from that which connects to the cathode of tube V2.

Transformers T2 and T4 in units IA and IB respectively are so connected relative to each other that when power is applied, the A.-C. potential of end 19 of transformer T2 relative to end a of said transformer is approximately in phase with the A.C. potential of end e of transformer T4 relative to end d of transformer T4.

P is a power plug for connection to an A.-C. power supply of suitable frequency, potential difference and current capacity. S1 and S2 are power supply switches, the former being connected between the power plug P and the primaries of all the power transformers of the driving circuit (said primaries being connected in parallel with each other) and the latter switch S2 being connected between switch S1 and transformers T2 and T4 in such a manner as to permit disconnecting the power supply from the primary windings of transformer T2 and T4 without disconnecting said power supply from the primary windings of the other transformers T1 and T3.

The operation of the circuit as a whole is as follows:

When plug P is connected to a suitable A.-C. power supply and switch S1 (but not S2) is closed, the filaments and cathodes of tubes V1 and V2 become heated and the circuit is ready for operation. Keying is then effected by closing switch S2. When S2 is closed, end a of the secondary of transformer T2 becomes alternately positive and negative relative to end I). When end a is sufiiciently positive relative to end 29 so that the anode of tube I is substantially more positive than its cathode. tube V1 permits electrons to flow from its cathode to its anode and thence through resistor R1,. secondary of transformer T2 and to the plate c of condenser Cm which is thus charged with plate 0 negative relative to ground. During the portion of the cycle when Cm is being charged, the grid of tube V2 in unit 2 is sufficiently negative to prevent tube V2 from conducting current so that unit IB has no appreciable effect on the charge on condenser Cm during said portion of the cycle.

When the grid end of the secondary of transformer T4 is sufficiently positive relative to the other end of said secondary, tube V2 conducts electrons from cathode to anode thereby permitting Cm to discharge rapidly through the discharge circuit so that most of the energy which Cm stores is transferred to the transducer. During the discharge of Cm, condenser C2 is charged. the side of C2 electrically connected to the cathode attaining a positive potential relative to the other sid of C2. This charge on condenser C2 is substantially greater than the peak potential difference across the secondary of transformer T4 and is sufficient to provide a negative grid bias for V2 even while the grid end of the secondary of transformer T4 is becoming more positive relative to end (1, thereby enabling the grid of tube V2 to regain control of tube V2 as soon as the discharge of Cm is completed.

Condenser C2 discharges through resistor R2 at such a rate that the grid bias of tube V2 will not become positive or insufficiently negative to prevent conduction through said tube until nearly a full period of the impressed power supply after the discharge through tube V2 takes place. Thus the discharge through tube V is limited to one unidirectional pulse during each period of the power supply. The necessity for such a limitation arises from the fact that the transducer driven by this driving means oscillates mechanically for an interval after each driving pulse and by inverse action of said transducer an alternating voltage is caused to appear at the plate of V during such mechanical oscillation. It is essential that repeated discharges of the tube V2 at one or more instances of positive excursion of its plate potential during any interval between driving pulses be prevented. This applicants accomplish by the utilization of the combination R2C2 to apply a negativ potential to the grid of V2 immediately after the completion of each of said driving pulses.

During the time when tube V2 is conducting,

the anode of tube V1 is maintained negative relaever, when the anode of tube V1 again become-s positive relative to its cathode, the cycle of operation, comprising the charging and subsequent discharging of condenser Cm, is again started, and this cycle is carried out periodically at the frequency of the impressed power supply.

The basic concept of this invention lies in the charging of a condenser from a power supply and a rectifier in combination, and the discharging of said condenser through a transducer by means of a valve which controls the time of said discharging and limits it to periodic unidirectional pulses.

A modification of the fundamental circuit of unit IA of Fig. 1, which in no way conflicts with the objects or the embodiment of the invention as already set forth, is shown in Fig. 2. In this figure the tube V3 is a mercury vapor rectifier tube having a control grid, K is a key and the parts of the circuit labelled R1, T1. and T2 are identical in function to the parts of the same 4. to ground. The point at which R4 and R5 are connected together is at a negative potential between that of the point f andground II when key K is open but is at ground potential when key K is closed. Since the grid of tube V3 is connected through the resistor R6 to the junction of resistors R4 and R5, a negative potential is applied to said grid so long as key K is open, and said grid is grounded through resistor R6 when said key is closed. The tube V2 has such char acteristics that a sufiicient negative bias, such as that applied to it with the key K open, prevents it from conducting electrons from its cathode to its anode, and such that zero grid potential permits said tube to operate as a rectifier. Thus K serves to key the circuit. When the circuit of Fig. 2 is employed in place of unit IA of Fig. 1, switch S2 of Fig. 1, may be omitted or may be kept closed.

Various modifications in the circuit may be made without in any way conflicting with the basic concepts .of this invention. For instance,

the electrical ground H may be moved to any desired point in the circuit, and the sequence of the various elements in tracing around either the charging or the discharging circuit may be altered in various ways. Transformers T1 and T3 may be supplied from a separate power supply of different frequency from that which supplies transformers T2 and T4, Or transformers T1 and T2 may be omitted and batteries used in their places to supply filament or heater current.

According to the provisions of the patent statutes, we have set forth the principal mode of operation of our invention and have illustrated and described what we now consider to represent its best embodiments. However, we desire to have it understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically illustrated and described. 7

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of anyroyalties thereon or therefor.

We claim:

1. Means for driving an electro-acoustic transducer, comprising a charging circuit, a discharging circuit, said charging and discharging circuits including a first capacitor as a common part of both circuits, said charging circuit including a first rectifier, means for impressing an alternating potential difference on said rectifier whereby said capacitor will be charged once during each cycle of said alternating potential difference, said discharge circuit including said transducer, a second rectifier, and a second capacitor in circuit therewith and providing for the discharge of said first capacitor inless than a half-cycle of said alternating potential difference, a grid for said second rectifier, a control circuit for said grid, said control circuit including means for impressing an alternating bias potential on said grid in phase opposition to the first named alternating potential, and means for impressing a further bias potential of periodic exponential form on said grid, said means for impressing said further bias potential on said grid comprising said second capacitor, means actuated by the discharge of said first capacitor to charge said second capacitor, whereby upon the cessation of said discharge said second capacitor will impress a negative potential on said grid in excess of said alternating bias potential difference "and thus render said second rectifier non-conducting, and means providing for the dissipation of said charge on said second capacitor at a predetermined rate, whereby when said alternating bias has progressed through its negative half and again becomes positive, said exponential bias potential will have become insufficient to hold said grid negative throughout the positive half cycle of said alternating bias potential.

2. Means for driving an electro-acoustic transducer, comprising a charging circuit, a discharging circuit, said charging and discharging circuits including a first capacitor as a common part of both circuits, said charging circuit including a first rectifier, means for impressing an alternating potential difierence on said rectifier whereby said capacitor may be charged once during each cycle of said alternating potential difference, a grid for said first rectifier, means for impressing a negative potential on said grid relative to the cathode of said first rectifier to prevent operation of said first rectifier, means for removing said negative potential from said grid of said first rectifier to permit operation of said first rectifier, said discharge circuit including said transducer, a second rectifier, and a second capacitor in circuit therewith and providing for the discharge of said first capacitor in less than a half-cycle of said alternating potential, a grid for said second rectifier, a control circuit for said grid, said control circuit including means for impressing an alternating bias potential on said grid and means for impressing a further bias potential of periodic exponential form on said grid, said means for impressing said further bias potential on said grid comprising said second capacitor, means actuated by the discharge of said first capacitor to charge said second capacitor, whereby upon the cessation of said discharge said second capacitor will impress a negative potential on said grid in excess of said alternating bias potential difference, and means providing for the dissipation of said charge on said second capacitor at a predetermined rate, whereby when said alternating bias has progressed through its negative half and again becomes positive, said exponential bias potential will have become insufficient to hold said grid negative throughout the positive half cycle of said alternating bias potential.

3. Means for discharging a capacitor periodically through an electro-acoustic transducer, in one uni-directional pulse each period, such means comprising a discharge circuit in series with said capacitor, said discharge circuit comprising said transducer, a rectifier, a second capacitor in circuit therewith, a grid for said rectifier, a control circuit for said grid, said control circuit including means for impressing an alternating bias potential on said grid, and means for impressing a further bias potential of periodic exponential form on said grid, said means for impressing said further bias potential on said grid comprising said second capacitor, means actuated by the discharge of said first capacitor to charge said second capacitor, whereby upon the cessation of said discharge said second capacitor will impress a negative potential on said grid in excess of said alternating bias potential difference, and means providing for the dissipation of said charg on said second capacitor at a predetermined rate, whereby when said alternating bias has progressed through its negative half and again becomes positive, said exponential bias potential will have become insufiicient to hold said grid negative throughout the positive half cycle of said alternating bias potential.

4. Means for driving an electro-acoustic transducer,'comprising a charging circuit, a discharging circuit, said charging and discharging circuits including a first capacitor as a common part of both circuits, said charging circuit including a first rectifier, means for impressing an alternating potential difference on said rectifier whereby said capacitor will be charged once during each cycle of said alternating potential difference, said discharge circuit including said transducer, a second rectifier, and a second capacitor in circuit therewith and providing for the discharge of said first capacitor in less than a half-cycle of said alternating potential difference, a grid for said second rectifier, a control circuit for said grid, said control circuit including means for impressing an alternating bias potential on said grid, said bias potential being in such phase as to bias said grid'negative during the charging portion of the cycle'of said alternating potential difierence, and means for impressing a further bias potential of periodic exponential form on said grid, said means for impressing said further bias potential on said grid comprising said second capacitor, means actuated by the discharge of said first capacitor to charge said second capacitor, whereby upon the cessation of said discharge said second capacitor will impress a negative potential on said grid in excess of said alternating bias potential difference, and means providing for the dissipation of said charge on said second capacitor at a predetermined rate, whereby when said alternating bias has progressed through its negative half and again becomes positive, said exponential bias potential will have become insufiicient to hold said grid negative throughout the positive half cycle of said alternating bias potential.

5. Means for driving an electro-acoustic transducer, comprising a capacitor, a first rectifier in circuit therewith, means impressing an alternating current voltage on said rectifier whereby said capacitor will be charged once during each cycle of said alternating current, a discharge circuit for said capacitor including said transducer, a second rectifier in said discharge circuit, a control grid in said second rectifier, means impressing said alternating current voltage on said grid, whereby said rectifier will be rendered conducting once during each cycle of said alternating current and said capacitor will thereupon discharge therethrough, and means impressing a, negative potential on said grid thereby rendering said second rectifier non-conducting upon the completion of said discharge and maintaining it in that state until said capacitor has again been charged.

6. Means for driving an electro-acoustic transducer, comprising a capacitor, a first rectifier in circuit therewith, means impressing an alternating current voltage on said rectifier whereby said capacitor will be charged once during each cycle of said alternating current, a discharge circuit for said capacitor including said transducer, a second rectifier in said discharge circuit, a control grid in said second rectifier, means impressing said alternating current voltage on said grid, whereby said rectifier will be rendered conducting once during each cycle of said alternating current, and said capacitor will thereupon discharge therethrough and means operated by said discharge to impress a negative potential on said grid upon the cessation of said discharge there-by "rendering said second rectifier non-conducting,

and maintaining said negative potential on said grid for a predetermined time.

7. Driving means for utilizing an alternating current voltage to impress upon an electroacoustic transducer a series of driving pulses shorter than a half-cycle of said voltage and for maintaining said transducer electrically isolated from said driving means during the inter vals between said impulses, said means comprising a capacitor, means for charging said capacitor throughout alternate half-cycles of said voltage, means for discharging said capacitor through said transducer during the remaining half-cycles of said voltage, said discharging means including a rectifier, a control circuit for said rectifier, and means actuated by the discharge of said capacitor to apply a blocking voltage to said rectifier and to maintain said dis charge means blocked for the duration of one of 20 said intervals.

,8. Driving means utilizing an alternating current voltage to impress upon an electro-acoustic transducer a series of driving impulses shorter than a half-cycle of said voltage and for maintaining said transducer electrically isolated from said driving means'durlng the intervals between said impulses, said means comprising a capacitor, means for charging said capacitor throughout alternate half-cycles of said voltage, a discharge circuit for said capacitor, said discharge circuit including a, rectifier and said transducer, said discharge circuit providing for the discharge of said capacitor in less than a half-cycle of said alternating current voltage, a control grid for said rectifier, means actuated by the discharge of said capacitor to apply a blocking voltage to said grid during the intervening half-cycles of said alternating current voltage thereby rendering said rectifier non-receptive to energy fed back from said transducer following the completion of said discharge, for a periodof time equal to the duration of one of said intervals.

HARVEY C. HAYES. HAROLD L. SAXTON. 

